1. Field of the Invention
The present invention relates to a measuring timer system for measuring the period of input pulse signals, particularly to measurement of a slight error of the period when the period value is roughly estimated.
2. Description of the Prior Art
FIG. 3 shows a circuit block diagram of an existing measuring timer system for measuring the period of input pulse signals. In FIG. 3, numeral 1 is a timer for measuring the period of input pulse signals, 2 is a measurement result register for holding measurement results, and 1S is a switch.
FIG. 4 shows the timing for measurement.
The following is the description of operation. When the input pulse signal changes (point "a" in FIG. 4) (detected at the leading edge of the input pulse signal), the timer 1 is reset to start counting from the initial value. When the input pulse signal changes next (point "b" in FIG. 4), the switch 1S is turned on to hold the then counted value as a measurement result before resetting the timer 1. The above operation is repeated every input pulse signal period.
A slight error may occur in the period of the input pulse signal. In this case, the error can accurately be measured by increasing the clock speed.
Problem to Be Solved by the Invention!
Because the existing measuring timer system is constituted as described above, the number of bits comprising the flip flop of the timer 1 must be increased by a value equivalent to the increase of the clock speed in order to accurately measure input pulse signal period. That is, when clock is high-speed, the value counted by the clock is unavoidably increased. Therefore, to correspond to the increase of the counted value., the number of bits of the timer must be increased.